Such systems for injecting fuel directly into the combustion chamber of an internal combustion engine are generally known. In this context, a distinction is made between a so-called "stratified operation" as a first operating mode and a so-called "homogeneous operation" as a second operating mode. The stratified operation is used particularly in the case of smaller loads while the homogeneous operation is used in the case of bigger loads placed on the internal combustion engine.
In the stratified operation, fuel is injected into the combustion chamber during the compression period of the internal combustion engine in such a manner that, at the time of ignition, a fuel cloud is in the immediate surroundings of a spark plug. This injection can be carried out in different ways. In fact, is possible for the injected fuel cloud to be near the spark plug during or immediately after the injection, and to be ignited by the spark plug. It is also possible for the injected fuel cloud to be conveyed to the spark plug by a charging movement, and to be ignited only then. In both burning methods, there is no uniform fuel distribution but a stratified charge.
The advantage of the stratified operation is that it makes it possible for the placed smaller loads to be executed by the internal combustion engine using a very small fuel quantity. Bigger loads, however, cannot be fulfilled by the stratified operation.
In the homogeneous operation intended for such bigger loads, fuel is injected during the induction period of the internal combustion engine, so that the fuel can still be swirled, and thus distributed in the combustion chamber without any problem. In this respect, the homogeneous operation corresponds more or less to the operating mode of internal combustion engines where fuel is injected into the intake pipe in a conventional manner. If required, the homogeneous operation can also be used for smaller loads.
In the stratified operation, the throttle valve in the intake pipe leading to the combustion chamber is wide opened, and the combustion is mainly controlled and/or regulated via the fuel mass to be injected. In the homogeneous operation, the throttle valve is opened or closed as a function of the required torque, and the fuel mass to be injected is controlled and/or regulated as a function of the air mass taken in.
In both operating modes, i.e., in the stratified operation and the homogeneous operation, the fuel mass to be injected is controlled and/or regulated additionally as a function of a plurality of further input variables to an optimal value in terms of fuel saving, exhaust reduction and the like. In this context, the control and/or regulation is different in the two operating modes.
It is required to switch over the internal combustion engine from the stratified operation to the homogeneous operation and back again. While in the stratified operation, the throttle valve is opened wide, and the air is consequently supplied in a substantially dethrottled manner, in the homogeneous operation, the throttle valve is opened only partially, thus reducing the supply of air. In this context, above all during the switchover from the stratified operation to the homogeneous operation, the capability of the intake pipe leading to the combustion chamber of storing air must be taken into account. If this is not taken into account, the switchover may lead to an increase in the torque delivered by the internal combustion engine.